exploding plastic storage tanks

[Gregor]

Originally Posted by Tom Line

I STRONGLY disagree that the only avenue of improving the potential safety issues around plastic pneumatics tanks is outlawing them. I would much rather see a numbers-driven problem solving method applied.

However, I can see vendors stepping away from supplying a 'safety' item like a sleeve since it becomes a question of liability if someone gets injured.

In an ideal world every safety precaution should be taken using all the advice given by the manufacturer and of that said here on Chief Delphi, but that simply does not happen. This is MUCH more dangerous than a HP sticking their hand into the field for half of a quarter of an eighth of a second, yet there are no strict rules on these tanks.

As said earlier in this thread, tanks hose clamped down passed inspection! There was a team at GTRE this weekend with the black Clippard tanks (which are better in terms of not needing fittings) on the bottom of their intake arms which extended beyond frame perimeter and were the first point of contact in high speed crashes with other robots! They passed inspection too.

The black tanks have their place in FRC if mounted correctly in the appropriate location, but the white tanks need to go. They've a hazard to everyone within 30 ft. of them. When teams (including my own) use them incorrectly, it's just a recipe for injury, and it's only a matter of time before someone seriously gets injured.

I've been hit by moving robots, smacked by robot arms, and had my fingers pinched in more robot mechanisms than I care to count, but none of these are even close to the potential danger of these tanks.

[yash101]

Originally Posted by Tytus Gerrish

this makes me want to test one to failure just to see that it takes to bust em

You wish
That seems very fun [and dangerous]. Do not try this at home!


I think the best sleeve would be a kit of the tank and sleeve so the strongest parts of the tank are the places uncovered. The rest should be contained. We are using mostly metal tanks, but we might (I can't properly recollect) have 2 plastic tanks!

What are these tanks made of? "Polymer" is quite wide of a material definition. It feels like PVC, but I doubt PVC is that strong!

[AndreaV]

Originally Posted by yash101

I think the best sleeve would be a kit of the tank and sleeve so the strongest parts of the tank are the places uncovered. The rest should be contained. We are using mostly metal tanks, but we might (I can't properly recollect) have 2 plastic tanks!

What are these tanks made of? "Polymer" is quite wide of a material definition. It feels like PVC, but I doubt PVC is that strong!

The old white tanks are made of pvc, a quick google search reveals the new tanks are made of polypropylene.

Rupturing tanks at 120 psi is not fun.. not in the slightest. While there have been (luckily) no serious injuries from exploding tanks, it can leave you quite shaken. The sound is nothing to sneeze at either, at GTRW many students had momentary hearing loss and ear pain that lasted into the next day just from being in close proximity of it going off, and this was in a large open area.

[MrBasse]

Polypropylene, not PVC.

From the FIRST blog last year:
Over the weekend, it was brought to our attention that a failure of the white polypropylene air tank, donated by Clippard (Clippard PN: AVT-PP-41, AndyMark PN: am-2007, FIRST Choice PN: fc13-100), had occurred.

[Trent B]

Originally Posted by AndreaV

The old white tanks are made of pvc, a quick google search reveals the new tanks are made of polypropylene.

The old tanks were also made of polypropylene: http://www.chiefdelphi.com/forums/sh...d.php?t=112396

As are Pneuaire air tanks.

[Jon Stratis]

Originally Posted by AndreaV

The old white tanks are made of pvc, a quick google search reveals the new tanks are made of polypropylene.

Rupturing tanks at 120 psi is not fun.. not in the slightest. While there have been (luckily) no serious injuries from exploding tanks, it can leave you quite shaken. The sound is nothing to sneeze at either, at GTRW many students had momentary hearing loss and ear pain that lasted into the next day just from being in close proximity of it going off, and this was in a large open area.

Correction. The old white tanks, Clippard PN AVT-PP-41, are polypropylene as well, not PVC. I am not aware of a single manufacturer that rates PVC for use in gas storage - PVC is generally only rated for liquid pressure.

[Moon2020]

Additionally, plastic becomes brittle with age.
It is why infant seats for cars have an expiration date.

We use Consequence vs. Likelihood in our 5x5 risk matrices.
All components that see 125 psi should be rated for 125 psi or above. There is a factor of safety already built into their rating. Make sure the PRV is calibrated properly. Is the gage calibrated properly?

The hazard is from the shrapnel created. The cause can be tank rupture due to: brittle plastic, over pressurization (not properly calibrated PRV), manufacturing flaw, design flaw, workmanship issues (assembly), damage from improper handling, mistreatment, environmental factors (temp, humidity, etc.), etc.

[Racer26]

Originally Posted by JamesCH95

No, no it wouldn't. See other posts in this thread about shrapnel puncturing ball covers without issue.

I think I posted something similar last year... but biaxial kevlar sleeve or similar would be required to provide even modest protection. Multiple layers would be required IMO, and a good way to keep the ends of the sleeve closed.

Edit: what velocity air flow is needed to exert a significant pressure on a fabric? Said fabric doesn't need to be air-tight to sustain significant loading in the event of a storage tank's catastrophic failure.

I realize what happened at GTR West and 1310's exploding tank puncturing their ball and killing a laptop.

I can't help but wonder, though, if even a bumper-fabric sleeve would eat a significant amount of the kinetic energy, when applied at the failure point (thereby partially inhibiting the extreme acceleration of the plastic shrapnel). Agreed that kevlar would be better, though.

[mman1506]

Originally Posted by FRC3883FRC

Our team had our tanks on our intake a very vulnerable position. We were highly highly HIGHLY recommended by the inspectors (almost to the point of not passing) to cover our tanks. We simply added bumper material over both of the tanks. They still fit right in the same c claps they some with and they dont look all that bad. A couple zip ties and the bumper fabric and we were good to go. You can see in the video that our robot has two red tubes at the top of the intake and around 9 seconds in you can see why they highly recommended covering them up.
Here is the video.
http://www.youtube.com/watch?v=nvAFL...u8USGMhWY2qgkw
If you are using these tanks make some covers or make sure they are in a very safe location.

1310 had an air tank explode in their pit and the pieces went right through the FRC Ball puncturing 2 layers of fabric and rubber without slowing it down. I doubt the bumper fabric would be able to contain it.

[thefro526]

Originally Posted by Jared Russell

In one case, the problem was a student over-tightening a fitting to the plastic threads. In another case, we believe that Loctite was used on the fitting threads.

Thankfully, the new (for 2014) Black Clippard Tanks that AM sells have a push to connect fitting that should (in theory) eliminate any failures that the connection point, or at the very least cause the hose to pop off before the tank fails. Otherwise, over tightening of threads, especially NPT threads into plastic is an issue that's difficult to make 100% fool proof.

Originally Posted by mman1506

1310 had an air tank explode in their pit and the pieces went right through the FRC Ball puncturing 2 layers of fabric and rubber without slowing it down. I doubt the bumper fabric would be able to contain it.

Assuming the proposed sleeves all are wrapped reasonably tightly around the tanks, it shouldn't take much to contain a tank failure pretty well. In the instance you mention, it sounds like the tank burst and the pieces of shrapnel were allowed to accelerate to some speed (becoming projectiles) and then they punctured the ball. Assuming you're containing the failure as it happens, the chances of getting projectile type shrapnel will be significantly lower (since they'll be slowed as they contact/break through the sleeve) and if anything does mention to get past the sleeve, it will be traveling significantly slower than if the sleeve were not there.

------

We're actually running two of the black clippard tanks on our robot now, and haven't had any issues. Our mounting is fairly simple, we ran a strip of adhesive backed rubber down one of our metal structural members and then ziptied the tank to the member. The rubber does a pretty good job of holding the tank snug while also allowing it to have a bit of cushioning.

[DanielPlotas]

Originally Posted by mman1506

1310 had an air tank explode in their pit and the pieces went right through the FRC Ball puncturing 2 layers of fabric and rubber without slowing it down. I doubt the bumper fabric would be able to contain it.

The ball was punctured by pieces already moving at considerable speeds, but the fabric would be able stop them before they get moving.

[Jared Russell]

I have witnessed this in person twice (both times in 2013) and thankfully nobody was hurt either time. But they probably could have been.

In one case, the problem was a student over-tightening a fitting to the plastic threads. In another case, we believe that Loctite was used on the fitting threads.

Last year I proposed a mandatory sleeve in this post. I think it would be a cheap, easy, and effective harm reduction measure (though it would certainly need to be well-tested)...and it would let teams color their air tanks however they see fit

[donkehote]

Originally Posted by Jon Stratis

and I heard there was a tank that blew in week 1 as well.

One of 1310's tanks blew at GTR west. One of the mentors was tightening a fitting into the tank with the tank inflated to 120 psi try to eliminate a leak. The tank exploded in the mentors hands, (thankfully no injury's) and destroyed the laptop that was below the tank, aswell as popping one of their balls. The shrapnel was sent flying all the way to the roof of the fieldhouse, and was quite a shock to those at the event.

PLEASE ensure that if you are using the tanks, that you do not over tighten the fittings. I highly recommend pipe dope (thread sealant paste) for the plastic tanks. It allows you to tighten the fittings less while maintaining a good seal.

something like this

http://www.henkelna.com/product-sear...=8797874651137

The tanks are both a blessing and a curse, please treat them with care, as both inexperienced students and "experienced" mentors have fallen victim to these tanks.

[Steve W]

Originally Posted by donkehote

One of 1310's tanks blew at GTR west. One of the mentors was tightening a fitting into the tank with the tank inflated to 120 psi try to eliminate a leak. The tank exploded in the mentors hands, (thankfully no injury's) and destroyed the laptop that was below the tank, aswell as popping one of their balls. The shrapnel was sent flying all the way to the roof of the fieldhouse, and was quite a shock to those at the event.

I spoke to the mentor involved within a minute of the explosion. He told me that he had tightened the tank and was testing the tank when it exploded. I may be wrong but if he was tightening when it exploded he would have had shrapnel in his hands or body. There was enough force to blow the top off of a laptop and throw plastic everywhere and he had only a small minor cut on one of his hands. There are many "stories" going around about what happened. Please don't pass around hearsay.

That said, air pressure is nothing to play around with. As we have seen an many posts about exploding tanks this year, safety MUST be taken when using pneumatics. Many people are trying to find a way around the Safety Rules by saying they are not rules. In FIRST we do not want to see people injured. We want FIRST to be a positive experience for everyone. Losing a part of your body or an eye is NOT a positive experience. I know, it won't happen to you, but we don't want to take a chance. Some rules are maybe a bit overboard but I would rather have that than have someone hurt because of lack of rules.

[Tytus Gerrish]

as a person whom has had PVC explode in my hands I would like to testify that you won't necessarily get pvc shrapnel damage to your body